1. Field of the Invention
The present invention relates to a warper and, more precisely, to a device for measuring the running distance of a yarn, and a stop control device for a warper which ascertains an abnormal portion in a yarn and facilitates the repair of the abnormal portion in the yarn.
2. Description of the Prior Art
A warper referred to herein is a machine used for evenly arranging a desired number of yarns at prescribed intervals (a "warp") and taking them up around a drum or a warp beam while applying a prescribed tension on each yarn. The number of yarns, the dimension of intervals, the degree of tension and such other conditions are appropriately set to weave fabric.
When an abnormality, such as fluff or breakage, occurs in a yarn, it is necessary that a warper be halted automatically and the yarn immediately repaired, since an abnormality may cause problems such as hindering the weaving process or deteriorating the quality of a fabric.
Repairing abnormal yarns in a warper is not an easy operation. A yarn continues to run a considerable distance due to inertia from the time of detection of an abnormality until the warper stops. The running distance from the time of detection of an abnormality varies and depends on parameters such as the wind-up diameter of the warp beam and the running speed of the warper. Therefore, it is not easy to find the location of the abnormality in a yarn (hereinafter simply referred to as "abnormality"), after the warper stops.
With regard to the above problem, Japanese Laid-Open Patent Publication No. 46576/1983 discloses a method for simplifying the repair operation by controlling the running distance of a yarn from the time of detection of an abnormality until the warper stops so that the location of the abnormality is always the same after the warper has halted. The invention disclosed in the above mentioned Patent Publication calls for detecting the wind-up diameter of the warp beam and the running speed of the warper and controlling the brake of the warper. Based on the data detected, one can control the braking force of the warper as to make the running distance of the yarn constant. The desired braking force is calculated based on the moment of inertia of the warp beam and the running speed of the warper.
As a rule, the braking force of a brake cannot be drastically changed. Therefore, the conventional art described above presents a problem because it is extremely difficult to stop the warper in such a manner so that the site of the abnormality is always at the same position. This is because a brake used in a warper is usually a mechanical brake consisting of a brake shoe and a brake drum, and it is extremely difficult to precisely produce an intermediate braking force of desired magnitude even though the force applied to the brake shoe can be controlled. This problem may be overcome by using an eddy-current brake or a similar device which is capable of producing any desired braking force. On the other hand, using an eddy current brake or similar device makes the entire machine very expensive to fabricate.